This invention relates to relief or by-pass valves for disposable spin-on type fluid filter assemblies, such as lubricant and working fluid filter assemblies for vehicular and industrial applications. Such relief valves, in response to a predetermined fluid pressure, generally resulting from pump surges on start-up or from filter medium plug up, open to allow fluid to by-pass the filter medium and thus assure an adequate supply of fluid downstream of the filter assembly and/or prevent rupture of the filter medium.
Generally, these relief valves are comprised of a biasing means, such as a helical coil spring which maintains a seal member in sealing engagement at a predetermined resilient loading with a plurality of fluid flow openings. Examples of such relief valves for fluid filter assemblies are shown in U.S. Pat. Nos. 3,061,101 and 3,156,259.
The helical spring in the valves shown in these patents is confined between the seal means and an integral portion of the valve body, i.e. the member containing the flow openings, to maintain the seal means in sealing engagement with the flow openings under normal conditions.
The valve body shown in U.S. Pat. No. 3,061,101 is formed of metal and the valve body shown in U.S. Pat. No. 3,156,259 is formed of a moldable plastic having a high temperature melting point relative to many other plastics. Use of a moldable plastic for the valve body is highly desirable as it permits rapid and economic forming of the relatively complex configuration generally required for such valve bodies. Also, use of moldable plastic enables economic formation of integrally molded flexible members which extend from the valve body to retain the springs. Small cross section flexible members are preferable as they facilitate construction, minimize any impediment to fluid flow and provide a material savings. However, under some circumstances, such as when a relief valve is exposed to high temperature fluid flow, plastic members having a relatively small cross section may lose strength and elongate, or even break, due to the constant force of the spring they are confining. Such elongation or breakage would not be readily detectable and would cause a large amount or in the case of breakage, virtually all, of the fluid to by-pass the filter element.
Additionally, to achieve manufacturing efficiency, it is desirable to form and maintain the separate components of a relief valve as a unitized subassembly to facilitate assembly of the valve into a complete filter assembly.